In certain types of vehicles, such as medium and heavy duty trucks, it is advantageous to provide the electrical system with multiple electrical generating machines, which are alternators or generators depending on whether the electrical system uses alternators or generators. For example, for utility and up-fitted trucks that use on 12V battery, many applications require the use of a dual alternator system. This can generate about 400 A of current that can feed on-board electric devices (such as electric devices on emergency vehicles) without compromising battery life, state of charge (SOC) of the battery, and depth of discharge (“DOD”) of the battery. For convenience the discussion herein will be the context of alternators, it being understood that it also applies to generators.
A voltage regulator is used to regulate the output voltage of the alternator. Typically, the voltage regulator varies the voltage of the field of the alternator to regulate the output voltage of the alternator. In many applications, the alternator has an internal voltage regulator.
In certain applications having a single alternator, an external electronic voltage regulator has been used. In one such application, the external electronic voltage regulator is implemented in the electronic control unit (ECU) that is also used as the engine control module of a vehicle. In this application, the external voltage regulator outputs a pulse width modulated drive signal to the field winding of the alternator and varies field voltage of the alternator to regulate the output voltage of the alternator by varying the duty cycle of the pulse width modulated signal. As used herein, an “electronic voltage regulator” is a device that generates a pulse width modulated drive signal that is used to energize the field windings of an electrical generating machine. The device is for example implemented in hardware or a combination of hardware and software. The device is for example a stand-alone device or is for example implemented as part of another device, such as the engine control module of a vehicle. The electronic voltage regulator for example generates the pulse width modulated drive by directly generating it or for example generates it by controlling another device, such as a power switching device by generating a pulse width modulated switching signal that is used to switch the power switching device.
FIG. 1 is a basic schematic showing the topology of a prior art electrical system 100 in which an external electronic voltage regulator is used to control the voltage of an alternator. Electrical system 100 is illustratively an automotive vehicle electrical system and is a part of an automotive vehicle, shown representatively by dashed box 102 in FIG. 1. The external electronic voltage regulator is illustratively implemented in an electronic control unit (“ECU”) 110, that is also the engine control module for vehicle 102. More specifically, electrical system 100 has an alternator 104, battery 106, power distribution center 108 and ECU 110 that is the engine control module. ECU 110 includes an electronic voltage regulator 112 that controls the field voltage of field windings 114 of alternator 104. A voltage output (B+) of alternator 104 is coupled through a fusible link 116 to a positive terminal 118 of battery 106. A negative terminal 120 of battery 106 is coupled to ground.
Electronic voltage regulator includes error signal generator 122, PI controller 124, PWM signal generator 126 and power signal driver 128, which is illustratively a high side driver and may be referred to herein as high side driver 128.
The control of alternator 104 is managed by the electronic voltage regulator 112 in ECU 110 based on voltage feedback sense line “B+ Sense” coupled to a “B+ sense” output of alternator 104, which is coupled to the internal voltage output of alternator 104 through a B+ resistor. This sense voltage is compared by error signal generator 122 to a target voltage determined by the ECU 110 based on various parameters known to the ECU 110 from other sensors in the electrical system 100 (not shown in FIG. 1), such as battery temperature, engine speed, engine load and others. The comparison between the sense voltage and the target voltage produces an error signal which is used by PI controller 124 of electronic voltage regulator 112 to calculate the duty cycle for a PWM drive signal applied to field windings 114 of alternator 104 to control the field voltage and thus regulate the output of alternator 104. The field windings 114 of alternator 104 are coupled to an output 130 of ECU 110 at which the PWM drive signal is generated. More specifically, PI controller 124 of electronic voltage regulator 112 determines the duty cycle at which to drive the field windings 114 of alternator 104 and outputs to PWM signal generator 126 the value of this duty cycle, which is the PWM value in FIG. 1. PWM signal generator 126 generates a PWM signal having this duty cycle which is used to switch high side driver 128, which turns on and off the field of alternator 104. High side driver 128 is coupled through contacts 132 of an automatic shutdown relay (ASD) 134 of power distribution center 108 and a fuse 136 of power distribution center 108 to positive terminal 118 of battery 106. High side driver 128 is illustratively a high power switching semiconductor device, such as an SCR, Thyristor, IGBT, power MOSFET, or the like. The objective of this control system is to minimize the error signal, which implies that the sense voltage is being controlled to achieve the target voltage. The PI loop in PI controller 124 of electronic voltage regulator 112 is calibrated to optimize the overshoot, undershoot and settling time performance specifications for system voltage response to various disturbances.